The present invention relates to a fire protection system for airplanes and particularly to a system for maintaining firewall integrity between the airplane wing strut structure and the jet engine supported thereby.
Jet engines are typically attached to the wing of an airplane by means of nacelle struts or pylons which enclose the pneumatic, electric, fuel and hydraulic connections to the engine as well as links and spars supporting the engine from the airplane wing. Struts are essentially frame and skin structures riveted and bonded together to form a torque box.
The airplane jet engine operates at high temperatures whereby a strut fire seal and firewall are desirably incorporated to protect the wing and upper strut systems from exposure to high temperatures and fire damage. Firewall continuity is desirably maintained with the stainless steel primary exhaust nozzle sleeve of the engine serving as a continuation of a strut firewall.
An engine fire must be contained and must not penetrate the adjacent strut structure. However, the unusual contour of the turbine exhaust nozzle can produce a gap which is uneven in dimension between the nozzle upper forward edge surface and the strut structure lower surfaces. The engine is, of course, very heavy and is subject to relative motion with respect to the airplane structure due to thermal and loading conditions.
Heretofore, various fire barrier means have been employed to avoid penetration of hot gases and flame in the event of an engine fire. In one instance a seal between the engine exhaust nozzle and the strut structure comprised an elastomeric "O-ring" section coated by fiberglass. However, this solution may not provide substantial compensation for varying dimensions. Also reliability and wear resistance may be in question. In another prior art system, a plurality of sheet metal spring fingers secured to the turbine exhaust nozzle structure contacted a seal depressor attached to the strut structure. Slots between fingers enabled the accommodation of some degree of nozzle/strut gap as well as compensation for the unique contours involved. However, the slots or spaces between the fingers could allow penetration of hot gases and flame to the strut area in the event of an engine fire whereby the intended fire barrier purpose is not accomplished.